Concrete is produced in such a manner that gravel, sand, cement and mixing water which are measured in accordance with predetermined composition are input into a mixer, and they are mixed for predetermined time. Various admixtures are added to the concrete produced in this manner. For example, water-reducing agent can reduce mixing water while securing flow property, and separation and reducing agent can reduce an amount of breeding. When it is desired to control setting and hardening time of concrete, retarder for delaying setting and hardening and promoter for promoting hardening are added. After concrete is produced, it is necessary to place the concrete within predetermined time, but if the setting and hardening time is adjusted, time constraint is reduced, and flexibility of producing and handling concrete is enhanced.